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The record for fastest manned flight was taken in 28 July 1976 by Capt. Eldon W. Joersz and Maj. George T. Morgan on the Lockheed blackbird SR-71 and was unbeaten for almost 40 years now, reaching a top speed of 3.5km/h. The plane was top secret at the time of the cold war and was designed for military observation and would sometimes outrun enemy missiles. Lockheed is now working on a new version the SR-72 able to reach hypersonic speed almost twice as fast as its predecessor.
There are 4 forces acting on a plane when it is flying; Thrust, drag, lift and weight. If the plane is traveling at a constant altitude then the lift and weight forces balances each other out while thrust keeps the plane going forward. You can see on the wing of a plane the bottom side is straight while top side is a bit curved. Lift is generated when air passing through the top side of the wing is faster compared to the bottom side. According to Bernoulli’s principle the increase in a fluids speed decreases pressure. And so when the planes speed increases during takeoff, the wings become more effective and the difference in pressure generates the lift.
And as the plane flies forward, a wall of still air collides with the plane producing drag or air resistance. Drag is countered by an aerodynamically shape/body. Less drag would mean a faster plane. Flying at sea level has more drag than higher levels of altitude because the air is denser at sea level, decreasing the possible top speed a plane can go. Of course the higher altitude a plane goes the less dense the air. This makes the control surfaces and the jet engine, requiring a great amount of intake air, less efficient.
Commercial planes fly at 10km or a bit higher if needed. Air enters the turbine which is then compressed before burned, shooting out a stream of incredibly fast hot air that thrusts the airplane forward. The SR-71 however can reach up to 25km. In front of the air inlet is a spike that shields the engine from the sonic blast.
The Concorde was dismissed in 2003 mainly due to high fuel costs, noise and couldn’t bring enough people to make that much of a profit. But Lockheed Martin’s future plans are to bring back supersonic transport to the public.
http://en.wikipedia.org/wiki/Drag_%28physics%29
http://www.explainthatstuff.com/howplaneswork.html
http://en.wikipedia.org/wiki/Bernoulli%27s_principle
https://www.google.com/search?q=blackbird+plane+height&ie=utf-8&oe=utf-8#q=blackbird+plane+altitude